pyridine solutions

Journal of Inorganic Biochemistry

VANADIUM

389

U N U S U A L P R O D U C T O B T A I N E D F R O M [VO(SaI-L-Trp)(H20)] IN

P06

H20/PYRIDINE SOLUTIONS

J. Costa Pessoa a, M. T. Duarte a, J.J.R. Frafsto da Silva a, R.D. Gillard b, C. Madeira a, P.M. Matias a and I. Tomaz a

aCentro Quimica Estrutural, Instituto Superior Tdcnico, Av. Rovisco Pais, 1096 LISBOA, PORTUGAL; bDepartment of Chemistry, University of Wales, P.O. Box 912, Cardiff CF1 3TB, U.K. Several studies concern the preparation and reactivity of vanadium complexes of N-salicylideneamino acids, and these may be considered as model systems for some reactions of pyridoxal-potentiated enzymes. The present communication deals with the preparation, characterization and reactions of [VO(SaI-L-Trp)(H20)] (I). Other related complexes are also prepared and characterized. From solutions of (I) in H20/pyridine, orange-brown crystals of (Hpy+)4(L+)2[V10028] (L + as in scheme 1) were isolated and characterized by X-ray diffraction. Vanadium(IV/V) is known to be one of the most active metal ions in 13-eliminations 13. Therefore a possible mechanism for this reaction involves the attack of a pyridine molecule at the 13-carbon atom of the tryptophan residue in (I). Two L + and four Hpy+ cations are the cotmter-ions of the decavanadate formed by oxidation of V(IV) by atmospheric oxygen.

C- o\V, O)

:

~

PY

u

~

CHE--N~/-~

~j/CH2

HI

X = pyorH20

( L +)

Scheme 1 1. Y..Murakami, H. Kondo and A.E. Martell, J. Am. Chem. Soc., 95, 7138, (1973). 2. F. Bergel, K.R. Harrap and A.M. Scott, J. Chem. Soc., 1101 (1962). 3.

J. Costa Pessoa, I. Cavaco, C. Madeira, M.T. Duarte, P.M. Matias and R.D. Gillard, 3rd GIPS Meeting in Inorganic Chemistry, SL 11, Senigallia, Italy, June 1995.

Acknowledgements. We thank Fundag~o Calouste Gulbenkian, Fundo Europeu para o Desenvolvimento Regional, Junta Nacional de Investigac~o Cientifica e Tecnol6gica, and program PRAXIS XXI: projects:

PRAXIS/2/2.1/QUI/151/94

and

PRAXIS/2/2.1/QUI/14/94/BIC/935.

PRAXIS/2/2.1/QUI/14/94,

and

grants:

PRAXIS/414.I/BIC/2715,